Usabilly

wed6sep2006—36w249d68%—05h35m00s—0utc

In a surprising study, Jakob Nielsen found out most (85%) of the learning gleaned from usability tests came from your first 5 user tests; 3 users tests will still give you a whopping 67% of the learning there is. He then goes on to advocate small and iterative testing over a single massive one (say, three tests with 3 users each and improvements in between instead of one lone test with 9):

You want to run multiple tests because the real goal of usability engineering is to improve the design and not just to document its weaknesses.